Electronic factors determining the reactivity of metal surfaces

Based on density functional theory calculations of H-2 dissociation on Al(111), Cu(111), Pt(111) and Cu3Pt(111) we present a consistent picture of some key physical properties determining the reactivity of metal and alloy surfaces. The four metal surfaces are chosen to represent metals with no d-bands, with filled d-bands and with d-states at the Fermi level. We show that electronic states in the entire valence band of the metal surface are responsible for the reactivity, which consequently cannot be understood solely in terms of the density of states at the Fermi level nor in terms of the empty d-states above it. Rather we suggest that trends in reactivities can be understood in terms of the hybridization energy between the bonding and anti-bonding adsorbate states and the metal d-bands (when present), and we demonstrate that a simple frozen potential based estimate of the hybridization energy correlates well with the calculated variation of the barrier height for the different metal surfaces.